Embodiments relate to a comparator circuit and methods thereof. Some embodiments relate to a comparator circuit which may compare three inputs.
A high-performance integrated circuit (IC) internally may use at least one comparator to achieve precise control and/or other various functions. Such a comparator may include two inputs. To achieve relatively more complex functions, a 3-input comparator may be used. Example FIG. 1 illustrates comparator circuit 100 to compare three inputs. Referring to FIG. 1, 3-input comparator circuit 100 may compare voltage V1 of a first signal with a lower one of voltage V2 of a second signal and/or voltage V3 of a third signal. Further, 3-input comparator circuit 100 may output a result of a comparison.
Voltage V2 of a second signal may be fixed and/or voltage V3 of a third signal may be increased from 0. When voltage V3 of a third signal may have a value within a range between 0 and voltage V2 of a second signal, voltage V1 of a first signal may be compared with voltage V3 of a third signal. On the other hand, when voltage V3 of a third signal may be higher than voltage V2 of a second signal, voltage V1 of a first signal may be compared with voltage V2 of a third signal. In accordance with results of a comparison, an output of a comparator circuit may be determined.
Comparator circuit 100 of FIG. 1, which may compare three inputs, may not achieve accurate comparison when voltage V3 of a third signal may be approximately equal to voltage V2 of a second signal. When the difference between voltage V3 of a third signal and voltage V2 of a second signal is relatively large, only one of second transistor Q2 and third transistor Q3 may be turned on. In this case, comparator circuit 100 may normally operate because second bias current I2 may flow through only one of second transistor Q2 and third transistor Q3, namely, through only a turned-on transistor. However, the difference between voltage V3 of a third signal and voltage V2 of a second signal may be relatively small, such that both second transistor Q2 and third transistor Q3 may be turned on. In this case, half of a second bias current I2 may flow through each of second transistor Q2 and third transistor Q3.
An offset between first emitter-base voltage VEB1 and second emitter-base voltage VEB2 may relatively increase. Since second bias current I2 may be divided into two completely-equal parts, an offset may correspond to VT×In(2) (VEB1−VEB2=VT×In(2)), where VT may reference a temperature constant and/or In may reference a natural logarithm. Where half of second bias current I2 flows through each emitter node of each of second transistor Q2 and third transistor Q3, there may be an offset of VT×In(2). If VT is approximately 25 mV, an offset may be approximately 17.3 mV. N transistors, for example n being a natural number greater than 2, may be used and/or an offset may increase to VT×In(n).
Accordingly, there is a need of a comparator circuit and methods thereof which may compare three inputs, which may be capable of securing relatively precise operation and/or which may achieve an enhancement in an operation range.